The ability of a camera to produce a photograph that faithfully depicts a scene is governed in large part by its optical performance. With respect to modern consumer electronic devices, such as portable computers (laptops, tablet computers, and smart phones), as well as in desktop computers, improvements in image quality have been achieved together with the use of higher megapixel image sensors that are being incorporated into relatively small or tightly confined spaces within the housing of the consumer electronics device. As the dimensions of the optical components shrink, including, for instance, the imaging lens itself and its distance to an image sensor at the focal plane, the photograph produced by the camera becomes more susceptible to slight deviations in position and alignment of the optical system components. For instance, slight changes in the alignment of a lens relative to the optical axis and relative to the image sensor can result in image quality degradation. Such misalignments can occur during manufacturing and, in particular, during component assembly of a camera module in which the lens may be integrated.
There are several technical variables that can be used to evaluate the optical performance of a camera based on the quality of the resulting photograph of picture. For instance, there are image processing techniques to measure the sharpness of a photograph. Sharpness is also typically monitored during an auto-focus process in which a sharpness value is calculated over a number of different image captures or frames, as the distance between a camera lens and a plane of the image sensor is changed. The auto-focus process, of course, attempts to find the optimum location of a moveable lens along the z-axis (optical axis) that yields the sharpest captured image. Another optical characteristic that is often evaluated is distortion, that is whether a geometric shape of the object has been distorted (e.g., where a straight line appears slightly curved).
There are measurements of optical characteristics that are performed on a camera component, such as a lens, during manufacture testing, to ensure that the specimens released to end users are within a given performance specification. One characteristic that is tested is that of optical tilt. The camera component is installed in a test fixture while aligned with a target test pattern, and high precision mechanical measurement components including a laser light source and mirrors are used together with the needed automatic test equipment to mechanically measure the tilt of the camera component.